1. Field of the Invention
The present invention relates generally to electronic circuits and, more particularly, to an improved sense amplifier.
2. Related Art
Sense amplifiers are widely used in many types of applications to detect and amplify signals. For example, sense amplifiers are used to detect signals generated by memory cells or by an array of logic gates, such as to produce the logical OR result (i.e., sum of products term) at the output terminals of a logical AND array. FIG. 3 illustrates an exemplary conventional sense amplifier 300.
One drawback of conventional sense amplifiers is their sensitivity to the semiconductor process variation referred to as threshold voltage mismatch (Vt mismatch). If the threshold voltage mismatch becomes excessive, the sense amplifier will not function properly (e.g., circuit failure) and can produce an erroneous output signal.
Another drawback of conventional sense amplifiers is the high source current that flows through the sense amplifier under certain conditions (e.g., as the source voltage increases). The high source current results in numerous problems, such as high substrate current, poor latch-up, and hot carrier injection issues for one or more components of the sense amplifier. If the sense amplifier is biased to limit this undesirable high current flow, the switching speed of the sense amplifier is degraded.
As a result, there is a need for a sense amplifier that is more tolerant to threshold voltage mismatch without requiring excessive source current or resulting in a severe degradation in speed.
The present invention provides a sense amplifier that mitigates the affect of threshold voltage mismatch while limiting the amount of source current through the sense amplifier.
In accordance with one embodiment, a sense amplifier circuit includes input terminals and a pair of inverting buffers coupled to the input terminals and having output terminals. A resistive element is coupled between the output terminals. One or more gain stages follow the inverting buffer pair and condition and amplify the output signal on one of the output terminals to provide an output signal of the sense amplifier. A circuit is coupled to a gain stage to limit the amount of current flowing through it.
In accordance with another embodiment, a method of mitigating threshold voltage mismatch in a sense amplifier includes providing a sense amplifier having a first and a second input terminal coupled to a pair of inverting buffers providing a first and a second output terminal. The sense amplifier further includes a first amplifier coupled to the second output terminal and adapted to provide an output signal of the sense amplifier through a second amplifier. The method further includes coupling a resistive element having a first and second end across the first and second output terminal, with the first end coupled to the first output terminal and the second end coupled to the second output terminal. The method may further include coupling a circuit to the first amplifier to limit the amount of current flowing through the first amplifier.